This invention pertains to the an of methods and apparatuses for directing the flow of polymeric material from a supply source to one or more shaping dies.
In the art it is known to provide means for directing the now of various types of polymeric material from a supply source such as an extruder to one or more shaping dies. There are several factors which affect how the material flows within the flow channel. Considerations of wall friction, stretching and compression of the material, pressure loss and clamping force are factored in flow channel construction. For example, wall friction tends to slow the flow of material near the walls so that the flow of material near the center is faster producing undesirable results.
European Patent Document No. 0 226 434 discloses a polymer sheet produced by advancing a workpiece of polymeric material in the longitudinal direction between two pairs of opposed working surfaces of a die, so that the material of the workpiece flows simultaneously in the longitudinal direction (Z) and the lateral direction (Y) while decreasing in thickness in the (X) direction. A first pair of working surfaces of the die include opposed protrusions that squeeze the workpiece more at the center than at the edges. In this disclosure, the outlet ends of the protrusions extend the entire width of the channel between the second pair of working surfaces and the workpiece is pressed between two protrusions
Japanese Patent Document No. 03270922 discloses a pair of truncated quadrangular pyramid-like projections provided in a converging die head. The width of each projection increases toward the efflux port and the top faces of the projections are nearly parallel to each other. The efflux port end of each of the projections is sloped away from the top face which provides a slight increase in depth of the flow channel.
Moving the material through turns or over/around object, may cause unpredictable visco-elastic effects. The problem of non-uniform material flow and undesirable visco-elastic effects are addressed in the present invention.
The present invention is directed to the downstream region of a flow channel in an apparatus for directing the flow of polymeric material from a supply source to one or more shaping dies. The inventive construction of the downstream region provides for increased uniformity of flow across the entire width of the exit orifice. The present invention is further directed to balancing the flow of polymeric material between two or more flow passages.
In accordance with the practice of the present invention, there is provided a new and improved method and apparatus for directing the flow of material from a supply source to one or more shaping dies.
More particularly, an apparatus for directing the flow of polymeric material from a supply source to one or more shaping dies includes a flow channel having an inlet communicating with a supply orifice for receiving the material. The flow channel is defined by opposite side walls, an upper wall, and a lower wall. The flow channel includes a downstream region having a first zone in flow communication with the inlet, and a second zone in flow communication with die first zone, the first and second zones being associated with a common centerline, the side walls of the second zone diverging in opposite lateral directions generally symmetrically about the centerline and associated with an angle, xcex1. The apparatus is characterized by a flow directing insert located within the second zone positioned adjacent to the lower wall, the flow directing insert having sloped side surfaces intersecting a generally planar top surface, the top surface being spaced from the upper wall in the second zone.
According to another aspect of the invention, the flow channel includes a third zone In flow communication with the second zone for directing the raw of the material into the one or more shaping dies, the lower wall of the third zone being generally flush with the top surface of the flow directing insert.
According to another aspect of the invention, the third zone includes an exit orifice the exit orifice being associated with a lateral width wherein the exit orifice width is greater than an associated maximum lateral width of the flow directing insert.
According to yet another aspect of the invention, the upper wall and the lower wall of the flow channel in the second zone are disposed at an angle xcex2 to one another to effect a gradual decrease in a channel height in the second zone.
According to yet another aspect of the invention, the downstream region of the flow channel includes a pair of diverging flow branches in flow communication with the inlet, each of the flow branches including a flow directing insert located within each of the second zones.
According to yet another aspect of the invention, a flow directing insert for use in an apparatus for directing the flow of polymeric material from a supply source to one or more shaping dies is provided. The flow directing insert is characterized by a lateral centerline, a generally planar top surface, a bottom surface, and sloping side surfaces extending between the bottom surface and the top surface.
According to yet another aspect of the invention, the flow directing insert is further characterized by an increasing lateral width in symmetrical manner relative to the lateral centerline.
One advantage of the present invention is the reduction of visco-elastic effects in the extruded material.
Another advantage of the present invention is the improved uniformity of flow of polymeric material across the entire width of an exit orifice.
Another advantage of the present invention is that the flow of material between two separate flow branches of a flow channel is balanced.
Another advantage of die invention is the reduction of the projected area of the region filled with the polymeric material which decreases the required clamping force for a predetermined flow rate.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following specification.